U.S. patent application number 12/931094 was filed with the patent office on 2012-06-21 for solid-state laser with multi-pass beam delivery optics.
Invention is credited to Jan Vetrovec.
Application Number | 20120155503 12/931094 |
Document ID | / |
Family ID | 46234384 |
Filed Date | 2012-06-21 |
United States Patent
Application |
20120155503 |
Kind Code |
A1 |
Vetrovec; Jan |
June 21, 2012 |
Solid-state laser with multi-pass beam delivery optics
Abstract
A laser system including two laser amplifier modules, each
comprising a solid-state laser gain material (LGM) disk, and a
multi-pass optical assembly comprising a plurality of relay
mirrors. The relay mirrors are grouped in two relay mirror groups.
Individual relay mirrors are arranged to pass a laser beam from the
first LGM disk to the second LGM disk and back to the first LGM
disk, and so on. The laser beam is amplified with each pass through
the LGM disk. The relay mirrors may be arranged to repeat the
process of passing the laser beam to and from the two LGM disks
arbitrary number of times until the desired laser beam
amplification is attained. At that point, the laser beam may either
released from the laser system, reflected back causing it to
retrace its path through the system. This configuration increases
the effective gain and improves laser power extraction.
Inventors: |
Vetrovec; Jan; (Larkspur,
CO) |
Family ID: |
46234384 |
Appl. No.: |
12/931094 |
Filed: |
January 24, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61336523 |
Jan 22, 2010 |
|
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|
Current U.S.
Class: |
372/95 ;
372/99 |
Current CPC
Class: |
H01S 3/094057 20130101;
H01S 3/0604 20130101; H01S 3/025 20130101; H01S 3/2325 20130101;
H01S 3/07 20130101; H01S 3/0941 20130101; H01S 2301/02 20130101;
H01S 3/0612 20130101 |
Class at
Publication: |
372/95 ;
372/99 |
International
Class: |
H01S 3/081 20060101
H01S003/081; H01S 3/08 20060101 H01S003/08 |
Claims
1. A laser system, comprising: two solid-state laser gain material
(LGM) modules, and a multi-pass optical assembly including a
plurality of pairs of relay mirrors, wherein a first mirror and a
second mirror of each pair of relay mirrors are positioned to cause
a laser beam from one of said LGM modules incident on the first
mirror to be reflected directly to the second mirror and to cause
the second mirror to reflect the laser beam directly to another of
said LGM modules for further amplification, said laser beam being
reflected back and forth directly between the LGM modules and each
of the respective pairs of the plurality of pairs of relay
mirrors.
2. The laser system of claim 1, wherein said multi-pass optical
assembly comprises two groups of relay mirrors, with the relay
mirrors in each group are being arranged in a circular
configuration.
3. The laser system of claim 1, further including an end mirror
arranged to reverse the direction of said laser beam.
4. The laser system of claim 1, further including an end mirror
arranged to cause said laser beam to reverse its direction and
substantially retrace its path through said multi-pass optical
assembly.
5. The laser system of claim 1, further including an end mirror and
an outcoupling mirror, said end mirror and said outcoupling mirror
arranged to form a laser resonator.
6. The laser system of claim 4, wherein said resonator is a stable
resonator.
7. The laser system of claim 4, wherein said outcoupling mirror is
a graded reflectivity coating.
8. The laser system of claim 5, wherein said resonator is an
unstable resonator.
9. A laser system, comprising: a first solid-state laser gain
material (LGM) disk, a second solid-state LGM disk, and a
multi-pass optical assembly including a plurality of relay mirrors;
said relay mirrors arranged in two groups, a first relay mirror in
the first group arranged to receive a laser beam from said first
LGM disk and to pass said laser beam to another relay mirror in
said second group; said another relay mirror in said second group
being arranged to pass said laser beam to said second LGM disk;
said second LGM disk being arranged to reflect said laser beam to
yet another relay mirror in the second group; said yet another
relay mirror in the second group being arranged to pass said laser
beam to still another relay mirror in said first group; said still
another mirror arranged to reflect said laser beam back to said
first LGM disk.
10. The laser system of claim 9, wherein said process of sending
said laser beam from said first LGM disk to said second LGM disk
and back to said first LGM disk is repeated at least one more
time.
11. The laser system of claim 9, further comprising an end mirror,
a quarter wave plate, and a Faraday rotator.
12. The laser system of claim 9, wherein said multi-pass optical
assembly comprises two groups of relay mirrors, with the relay
mirrors in each group are being arranged in a circular
configuration.
13. The laser system of claim 9, further including an end mirror
arranged to cause said laser beam to reverse its direction and
substantially retrace its path through said multi-pass optical
assembly.
14. The laser system of claim 9, further including an end mirror
and an outcoupling mirror, said end mirror and said outcoupling
mirror arranged to form a laser resonator.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS:
[0001] This application claims priority from U.S. provisional
patent application U.S. Ser. No. 61/336,523, filed on Jan. 23, 2010
and entitled "Solid-State Laser with Multi-Pass Beam Delivery
Optics."
FIELD OF THE INVENTION
[0002] The present invention relates to lasers and more
particularly to a solid-state laser or the like and a multi-pass
optical assembly.
BACKGROUND OF THE INVENTION
[0003] Solid-state disk lasers and the like are being used in many
new applications. Examples of such applications may include but are
not necessarily limited to military laser target illuminators or
designators and commercial laser material processing applications
such as cutting, welding, drilling or the like. Such applications
typically require laser powers between about 5 kW and about 10 kW.
A single solid-state disk laser may be able to generate enough
power for an industrial laser device; however, the amplifier disk
may be relatively thin, about 0.5 to 2.5 mm, which may translate to
a rather short gain length. Consequently, if a single solid-state
disk laser amplifier is used in a traditional single pass
resonator, such as the single-pass laser resonator 100 illustrated
in FIG. 1, the resonator gain would be too low to buildup enough
recirculating power to saturate the solid-state gain medium of the
disk laser 102. In FIG. 1, the solid-state disk laser (SSDL) 102
may be thermally coupled to a heat sink 104. Pump beams 106 may be
directed on the SSDL 102 to generate an amplified beam 108 directed
through an output coupler 110. A reflective coating 112 may be
disposed between the SSDL 102 and the heat sink 104 on a surface of
the SSDL 102.
[0004] The U.S. Pat. No. 7,463,667 granted on Dec. 9, 2008 to the
Applicant and incorporated herein by reference in its entirety
discloses a laser system including a solid-state laser gain
material (LGM) and a plurality of relay mirrors for multi-passing a
laser beam to and from the LGM. Referring now to FIG. 2, the laser
system 200 requires that for each laser beam pass to the LGM disk
206, two relay mirrors are used. It is well known in the art that
the surface accuracy of relay mirrors is limited to a fraction of a
laser wavelength, typically to about 1/20th a wave at 628 nm
wavelength. A wavefront of a laser beam reflected from such a
mirror is imparted at least some of the inaccuracy of the mirror
surface. As a results, the beam quality (BQ) of the laser beam is
significantly degraded with each reflection from a relay mirror. It
is therefore desirable to achieve laser amplification with fewer
relay mirrors. Furthermore, the configuration of relay mirrors
disclosed in the U.S. Pat. No. 7,463,667 limits the laser system to
only one LGM, thereby limiting the laser power output.
[0005] In summary, prior art does not teach a laser system with LGM
disks and multi-pass beam delivery optics capable of producing very
high average power with good beam quality which is also very
compact and robust. It is against this background that the
significant improvements and advancements of the present invention
have taken place.
SUMMARY OF THE INVENTION
[0006] In accordance with an embodiment of the present invention, a
laser system including two laser amplifier modules, each comprising
a solid-state laser gain material (LGM) disk. The system also
includes a multi-pass optical assembly including a plurality of
relay mirrors. The plurality of relay mirrors is grouped in two
relay mirror groups. Individual relay mirrors may be arranged to
pass a laser beam from the first LGM disk to the second LGM disk
and back to the first LGM disk. The laser beam is amplified with
each pass through the LGM disk. In particular, a first relay mirror
in the first group may be arranged to receive a laser beam from the
LGM disk in the first module (first LGM disk) and to pass the laser
beam to another relay mirror in the second group, which then passes
the laser beam to the LGM disk in the second amplifier module
(second LGM disk). Yet another relay mirror from the second group
then receives the laser beam reflected from the second LGM disk and
passes it to still another relay mirror in the first group. The
still another mirror may reflect the beam back to the first LGM
disk, and so on. The relay mirrors may be arranged to repeat the
process of passing the laser beam to and from the two LGM disks
arbitrary number of times until the desired laser beam
amplification is attained. At that point, the laser beam may either
released from the laser system, reflected back causing it to
retrace its path through the system. This configuration increases
the effective gain length of the laser system and greatly improves
laser power extraction.
[0007] In accordance with one embodiment of the present invention,
a laser amplifier system comprises two laser amplifier modules each
comprising a solid-state LGM disk. The system also comprises a
multi-pass optical assembly including a plurality of relay mirrors.
The plurality of mirrors is grouped in two groups. A first relay
mirror of a first group of relay mirrors may be positioned to cause
a laser beam injected into the system to be reflected into the LGM
of a first laser amplifier module and a second relay mirror of the
first group may be positioned to receive the amplified laser beam
reflected from the LGM. The second relay mirror of the first group
may reflect the beam onto a first relay mirror of the second group,
which in-turn that may reflect the beam into the LGM of a second
laser amplifier module. A second relay mirror of the second group
may receive the beam from the second laser amplifier module and it
may release it from the system. Alternatively, the second relay
mirror of the second group may reflect the laser beam onto a third
relay mirror of the first group, which may then reflect the laser
beam into the first LGM disk. A fourth relay mirror of the first
group may receive the beam reflected from first LGM disk and
reflect it onto a third relay mirror of the second group, which may
reflect it into the second LGM disk. A fourth relay mirror of the
second group may receive the laser beam from the second LGM disk
and it may release it from the system or reflect it onto a fifth
relay mirror of the first group, and so on. Additional relay
mirrors may be added and arranged to repeat the process of passing
the laser beam alternately to and from the two LGM disks arbitrary
number of times until the desired laser beam amplification is
attained before it is released from the system.
[0008] In accordance with another embodiment of the present
invention, a laser amplifier system comprises two laser amplifier
modules each comprising a solid-state LGM disk. The system also
comprises a multi-pass optical assembly including a plurality of
relay mirrors. The plurality of mirrors is grouped in two groups. A
first relay mirror of a first group of relay mirrors may be
positioned to cause an injected laser beam to be reflected into the
LGM of a first laser amplifier module and a second relay mirror of
the first group may be positioned to receive the amplified laser
beam reflected from the LGM. The second relay mirror of the first
group may reflect the beam through a Faraday rotator onto a first
relay mirror of the second group, which in-turn that may reflect
the beam into the LGM of a second laser amplifier module. A second
relay mirror of the second group may receive the beam from the
second laser amplifier module and directs it through a quarter wave
plate onto an end mirror. The end mirror reflects the laser beam
through the quarter wave plate back onto the second relay mirror of
the second group thus reversing its reversing its direction. The
laser beam now travels through the amplified system in reverse
direction and exists generally collinear with the injected beam. As
in the previous embodiment, additional relay mirrors may be added.
The additional relay mirrors may be arranged to repeat the process
of passing the laser beam alternately to and from the two LGM disks
arbitrary number of times until the desired laser beam
amplification is attained before reversing the laser beam direction
by the end mirror. Position of the Faraday rotator is preferably
approximately half way in the laser beam path through the system in
the forward direction, so that one half of the passes though the
LGM disks occurs before the Faraday rotator and the other half of
the passes though the LGM disks in forward direction occurs after
the Faraday rotator.
[0009] In a variant to this embodiment where additional relay
mirrors are added, the relay mirrors in each may be arranged in a
generally circular pattern, causing the laser beam path to execute
a three-dimensional trajectory in space. This variant permits a
very compact grouping of all the components.
[0010] In accordance with yet another embodiment of the present
invention, a laser resonator system comprises two laser amplifier
modules, and end mirror, and an outcoupling mirror. The end mirror
and the outcoupling mirror may be arranged to form a laser
resonator. Such a laser resonator may be either stable or unstable.
In addition, the outcoupling mirror may have a uniform, partially
reflective coating or a graded reflectivity coating. The laser beam
modules each further comprise a solid-state LGM disk. The system
also comprises a multi-pass optical assembly including a plurality
of relay mirrors. The plurality of mirrors is grouped in two
groups. A first relay mirror of a first group of relay mirrors may
be positioned to cause a laser beam from an outcoupling mirror to
be reflected into the LGM of a first laser amplifier module and a
second relay mirror of the first group may be positioned to receive
the amplified laser beam reflected from the LGM. The second relay
mirror of the first group may reflect the beam onto a first relay
mirror of the second group, which in-turn that may reflect the beam
into the LGM of a second laser amplifier module. A second relay
mirror of the second group may receive the beam from the second
laser amplifier module and directs it onto an end mirror. The end
mirror reflects the laser beam through back onto the second relay
mirror of the second group thus reversing its reversing its
direction. The laser beam now travels through the amplified system
in reverse direction and it is delivered back onto the outcoupling
mirror, where a predetermined portion of the beam energy is allowed
to pass through the mirror and released from the system. The
remaining portion of the laser energy is reflected by the
outcoupling mirror back onto the first relay mirror of the fists
group. As in the previous embodiments, additional relay mirrors may
be added and receive the laser beam from the second relay mirror of
the second group. The additional relay mirrors may be arranged to
repeat the process of passing the laser beam alternately to and
from the two LGM disks arbitrary number of times until the desired
laser beam amplification is attained before reversing the laser
beam direction by the end mirror.
[0011] The solid-state laser with multi-pass optical assembly of
the present invention, may be usable with or mounted on a mobile
platform, such a military vehicle or the like for applications that
may include, but are not necessarily limited to laser target
illuminators, designators or similar applications. The present
invention may also be used in commercial applications, for example,
material processing such as cutting, welding, drilling or like
purposes.
[0012] Other aspects and features of the present invention, as
defined solely by the claims, will become apparent to those
ordinarily skilled in the art upon review of the following
non-limited detailed description of the invention in conjunction
with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a block diagram of an example of a prior art
single-pass laser optical assembly.
[0014] FIG. 2 is an isometric view of an example of a prior art
laser system including a solid-state laser and a multi-pass laser
resonator.
[0015] FIG. 3 is a schematic diagram of a solid-state laser
amplifier with multi-pass beam delivery optics in accordance with
one embodiment of the subject invention.
[0016] FIG. 4 is a schematic diagram of a solid-state laser
amplifier with multi-pass beam delivery optics in accordance with
another embodiment of the subject invention.
[0017] FIG. 5 is an isometric view with a partial cutaway exposing
the components of a solid-state laser amplifier with multi-pass
beam delivery optics in accordance with a variant of the invention
shown in FIG. 4.
[0018] FIG. 6 is a cross-sectional view 6-6 of the solid-state
laser amplifier with multi-pass beam delivery optics of FIG. 5.
[0019] FIG. 7 is a diagram showing the beam path in the solid-state
laser amplifier of FIG. 5.
[0020] FIG. 8 is a schematic diagram of a solid-state laser
oscillator with multi-pass beam delivery optics in accordance with
yet another embodiment of the subject invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Selected embodiments of the present invention will now be
explained with reference to drawings. In the drawings, identical
components are provided with identical reference symbols in one or
more of the figures. It will be apparent to those skilled in the
art from this disclosure that the following descriptions of the
embodiments of the present invention are merely exemplary in nature
and are in no way intended to limit the invention, its application,
or uses.
[0022] "Laser gain medium" or "LGM" may refer to an optical
material having a host lattice doped with suitable ions, which may
be pumped by an external source of laser or other optical radiation
to a laser transition. Examples of host lattice material that may
be used in conjunction with the present invention may include
yttrium aluminum garnet (YAG), gadolinium gallium garnet (GGG),
gadolinium scandium gallium garnet (GSGG), lithium yttrium fluoride
(YLF), yttrium vanadate, phosphate laser glass, silicate laser
glass, sapphire or similar materials. The host material may be in a
single crystal form or in a poly-crystalline (ceramic) form.
Suitable dopants for such lasing mediums may include titanium (Ti),
copper (Cu), cobalt (Co), nickel (Ni), chromium (Cr), cesium (Ce),
praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu),
gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho),
erbium (Er), thulium (Tm), and ytterbium (Yb). Optical pump sources
may be selected based on the absorption characteristics of the
selected laser gain medium. For example, semiconductor diode lasers
may be used for the optical pump source. The present invention is
not intended to be limited to any specific lasing or laser gain
material, or a specific pump source.
[0023] "Undoped optical medium" may refer to an optical material
which is preferably substantially free of any substances that can
absorb optical pump radiation. The undoped medium may be of the
same host material as the laser gain medium but substantially not
doped. In some embodiments of the present invention, however,
undoped optical medium may be slightly doped with ions which may
absorb optical radiation at the wavelengths of the optical pump
and/or the laser gain transition, but are not pumped to a
population inversion. Undoped optical medium may be bonded to
selected surfaces of the laser gain medium by a fusion bond, or
diffusion bond, or other suitable means. Such bonds must be highly
transparent at the laser wavelength as well as pump wavelengths. A
refractive index of the undoped optical medium and the bond are
preferably closely matched to that of the laser gain medium. A
suitable bond can be produced by fusion bonding, diffusion bonding,
or optical contacting followed by heat treatment. Examples of
optical contacting followed by heat treatment are described in the
U.S. Pat. Nos. 5,441,803, 5,563,899, and 5,846,638 by Helmuth
Meissner. Optical medium of this type may be obtained from Onyx
Optics in Dublin, Calif. If the host medium is optical glass, doped
and undoped sections may be readily attached by fusion bonding
produced by casting. This process is available from Kigre Inc. in
Hilton Head, S.C. If the host material is in ceramic form, such
bond may be produced during a sintering process. An example of such
a process is available from Konoshima Chemical Company LTD of
Kagawa, Japan.
[0024] "ASE absorption cladding" may refer to an optical material
capable of absorbing optical radiation at the wavelengths of one or
more laser transitions in the laser gain medium. Examples of ASE
absorption materials may include glass (such as phosphate glass,
silicate glass, fluorophosphate glass), crystals, ceramics, RTV
rubber, epoxy polymers, laminates of these materials or similar
materials. These materials may be also doped with absorbing ions.
For example, ions which absorb radiation at about 1.06 micrometers
are primarily Cu.sup.2+, Sm.sup.3+, Dy.sup.3+,Cr.sup.4+, and
V.sup.3+.Cu.sup.2+. For example, ASE absorption claddings based on
polymeric compounds attached to laser gain medium with adhesives is
disclosed in U.S. Pat. No. 4,849,036 entitled "Composite
Polymer-Glass Edge Cladding for Laser Disks" by Powell et al. ASE
absorption cladding preferably has a refractive index closely
matched to that of the laser medium to prevent reflection from an
edge-cladding interface. In addition, ASE absorption cladding
preferably has a coefficient of thermal expansion closely matched
to that of the laser gain medium to reduce thermal stresses. ASE
absorption cladding may be bonded to selected surfaces of the laser
gain medium by an adhesive, fusion bond, diffusion bond, optical
contacting followed by heat treatment similar to that described
above with respect to the patent by Meissner, or other suitable
methods, such as the glass casting process available from Kigre and
the sintering process from Konoshima previously discussed. Such
bond is preferably highly transparent at the laser wavelength and
with a refractive index closely matched to that of the laser gain
medium.
[0025] "ASE absorption coating" may refer to a thin film bonded
onto selected surfaces of the laser gain medium and/or undoped
optical medium and having the capability to absorb optical
radiation at the wavelengths of one or more laser transitions in
the laser gain medium. Such a thin film may be a combination of
materials which may have indices of refraction which are greater
than the index of refraction of the laser gain medium. Examples of
materials may include germanium, silicon, gold, silver, silica,
diamond, graphite, dried graphite ink, and some semiconductors and
halides. An ASE absorption coating may be produced and applied in
accordance with U.S. Pat. No. 5,335,237 entitled "Parasitic
Oscillation Suppression in Solid State Lasers Using Absorbing Thin
Films" by Zapata et al.
[0026] "Composite LGM" may refer to an assembly comprising at least
one component made of laser gain medium material, and at least one
component made of a group that may include the following materials:
1) an undoped optical medium, 2) an ASE absorption cladding, and 3)
an ASE absorption coating. In addition, the gain medium assembly
may have reflective, antireflective, and/or dichroic coatings as
appropriate for operation as an amplifier of laser radiation.
[0027] "Optical aperture" may refer to a maximum transverse
dimension of a laser beam, which can be received, amplified, and
transmitted by LGM. The term "aperture" used herein may be
synonymous to the one used in optics, such as the diameter of the
objective of a telescope or other optical instrument.
[0028] "Diode bar" may refer to a source of optical radiation
suitable for pumping a laser gain medium to a laser transition
comprising a 1-dimensional array of semiconductor lasers comprising
one or more diodes. The diodes may be mounted in a common substrate
and placed on a heat exchanger.
[0029] Referring to FIG. 3, there is shown a laser amplifier system
300 in accordance with one embodiment of the subject invention. The
laser amplifier system 300 comprises two solid-state laser (SSL)
amplifiers 302a and 302b, and a multi-pass laser optical assembly
further comprising relay mirrors 318aa, 318ab, 318ba, and 318bb
arranged in relay mirror groups 304a and 304b respectively
comprising relay mirrors 318aa and 318ab, and 318ba, and 318bb. The
laser amplifier system 300 further comprises an input mirror 386
and an output mirror 396. The relay mirror groups 304a and 304b
together may form a multi-pass optical assembly.
[0030] The amplifiers 302a and 302b may include a solid-state gain
material (LGM) disk 306a and 306b respectively. The LGM disks 306a
and 306b may be identical and each may include a lasing portion 308
and a perimetral portion 310. The perimetral portion 310 may
interface optically and mechanically with the lasing portion 308.
The perimetral portion 310 may be formed in a predetermined shape
to substantially prevent spontaneously emitted photons created in
the lasing portion 308 and entering the perimetral portion 310 from
returning to the lasing portion. Examples of LGM disks that may be
used for LGM disk 306 are described in U.S. Pat. No. 7,477,674,
entitled "High-Gain Solid-State Laser" issued to the Applicant et
al., on Jan. 13, 2009, and incorporated herein by reference in its
entirety and U.S. Pat. No. 7,085,304, entitled "Diode-Pumped Solid
State Disk Laser and Method for Producing Uniform Laser Gain,
issued to the Applicant on Aug. 1, 2006, and incorporated herein by
reference in its entirety.
[0031] The LGM disks 306a and 306b may form substantially a disk,
slab or other form. The lasing portion 308 and the perimetral
portion 310 may be integrally formed from a monolithic slab of
laser gain material which may be a preferred method of construction
if either neodymium, ytterbium, erbium, holmium, thulium or quasi-3
level ions are used for lasing. In another embodiment of the
present invention, the lasing portion 308 and perimetral portion
310 may be constructed from different materials as a composite
structure. The perimetral portion 310 may be made from an undoped
optical medium, ASE absorption cladding material similar to that
previously described, a combination thereof or a similar material.
Selected surfaces of the perimetral portion 310 may have ASE
absorption coating or the like. In such an embodiment, the
perimetral portion 310 may be secured to the lasing portion 308 by
diffusion bonding, fusion bonding, adhesive bonding, optical
contacting, co-sintering, or by other suitable technique. The LGM
disks 306a and 306b each may be placed on a suitable heat exchanger
(HEX) 332 to provide cooling and mechanical support. A laser diodes
328 may be used to inject power power into the disk and thus pump
the laser ions in the lasing portion 308 to a laser transition. A
reflective coating 312 may be disposed on a surface of lasing
portion 308 between the LGM disk 306 and the heat sink 332. The HEX
332 and the laser diodes may be further placed onto a common
support base 326.
[0032] In operation, laser diodes 328 inject optical power to the
lasing portions 308 and pump the laser ions to a laser transition,
thus producing laser gain in the lasing portions 308. An input
laser beam 314 may be injected into the multi-pass optical assembly
by the input mirror 386. The laser beam 314 may be initially
directed from the input mirror 386 to the relay mirror 318aa of the
relay mirror group 304a, and therefrom onto the lasing portion 308
of the LGM disk 306b where the beam is amplified and reflected to
the relay mirror 318ab the relay mirror group 304a. The relay
mirror 318ab reflects the laser beam 314 onto the relay mirror
318bb of the relay mirror group 304b, and therefrom onto the lasing
portion 308 of the LGM disk 306a where the beam is amplified and
reflected to relay mirror 318ba of the relay mirror group 304b. The
laser beam 314 may be reflected from relay mirror 318ba onto the
output mirror 396 and caused to exit from the laser system 300 as
an amplified laser beam 314'.
[0033] Alternatively, additional relay mirrors may be added and the
relay mirror 318ba may reflect the laser beam onto an additional
relay mirror. The additional relay mirrors may be arranged to
repeat the process of passing the laser beam alternately to and
from the lasing portions 308 of the two LGM disks 306a and 306b
arbitrary number of times until the desired laser beam
amplification is attained before the beam is delivered to the
output mirror 396 and exits from the laser system 300.
[0034] Referring now to FIG. 4, there is shown a laser amplifier
system 400 in accordance with one embodiment of the subject
invention. The laser amplifier system 400 comprises two solid-state
laser (SSL) amplifiers 402a and 402b, and a multi-pass laser
optical assembly with relay mirrors 418aa, 418ab, 418ba, and 418bb
arranged in relay mirror groups 404a and 404b respectively
containing relay mirrors 418aa and 418ab, and 418ba, and 418bb. The
laser amplifier system 400 further comprises an input mirror 486,
and end mirror 494, a quarter wave plate 474, and a Faraday rotator
476. The solid-state laser (SSL) amplifiers 402a and 402b may have
same construction and functionality as the SSL amplifiers 302a and
302b of FIG. 3. The relay mirror groups 404a and 404b together may
form a multi-pass optical assembly.
[0035] In operation, laser diodes 428 inject optical power to the
lasing portions 408 and pump the laser ions to a laser transition,
thus producing laser gain in the lasing portions 408. An input
laser beam 414 may be injected into the multi-pass optical assembly
by the input mirror 486. The laser beam 414 may be directed from
the input mirror 486 to the relay mirrors 418aa of the relay mirror
group 404a, and therefrom onto the lasing portion 408 of the LGM
disk 406b where the beam is amplified and reflected to the relay
mirror 418ab the relay mirror group 404a. The relay mirror 418ab
reflects the laser beam 414 through the Faraday rotator 476 onto
the relay mirror 418bb of the relay mirror group 404b, and
therefrom onto the lasing portion 408 of the LGM disk 406a where
the beam is amplified and reflected to the relay mirror 418ba of
the relay mirror group 404b. The laser beam 414 may be directed
from the relay mirror 418ba through the quarter wave plate 474 onto
the end mirror 494. The end mirror 494 may be arranged to reflect
the laser beam back through the quarter wave plate 474 back onto
the relay mirror 418ba thus causing the laser beam to reverse its
direction and retrace its path though the systems, becoming further
amplified, and eventually landing on the input mirror 486. The
input mirror 486 may now direct the laser beam out of the amplifier
system 400 as a laser beam 414' which may be collinear with the
input beam 414.
[0036] As in the system 300 of FIG. 3, additional relay mirrors may
be added and the relay mirror 418ba may reflect the laser beam onto
an additional relay mirror. The additional relay mirrors may be
arranged to repeat the process of passing the laser beam
alternately to and from the lasing portions 408 of the two LGM
disks 406a and 406b arbitrary number of times until the desired
laser beam amplification is attained before the beam is delivered
to the end mirror 494. In this case, the Faraday rotator 476 is
preferably relocated to a position approximately half way in the
laser beam path through the system in the forward direction, so
that one half of the passes though the laser portions 408 occurs
before the Faraday rotator and the other half of the passes though
the laser portions 408 in forward direction occurs after the
Faraday rotator. See, for example, Section 4.1.3 Nd:YAG Amplifier
in "Solid-State Laser Engineering," by W. Koechner, 5.sup.th
edition, published by Springer-Verlag, New York, N.Y., 1999.
[0037] Referring now to FIGS. 5 and 6 there is shown a laser
amplifier system 400' in accordance with a variant of the
embodiment of the subject invention shown in FIG. 4 and having
additional relay mirrors. The laser amplifier system 400' is
substantially same as the laser amplifier system 400 except that
the relay mirror groups 404a and 404b each are arranged in a
generally circular pattern. The circular patterns of the relay
mirror groups 404a and 404b are preferably on a common axis with
the laser modules 402a and 402b. In addition, the individual relay
mirrors 418 are shown being formed as facets on a common substrate
478. However, the invention also admits relay mirrors 418 being
formed as individual components. The circular arrangement of the
relay mirror groups 404a and 404b makes it easier to construct a
laser amplifier system suitable for a large number of laser beam
passes though the LGM disks, thus allowing for a very high
amplification. Furthermore, the circular arrangement of the relay
mirror groups permits a very compact grouping of all the
components. The SSL amplifiers 402a and 402b, the relay mirror
groups 404a and 404b, as well as the input mirror 486, end mirror
494, quarter wave plate 474, and the Faraday rotator 476 may be
mounted on an optical bench 466, which may be generally formed as a
cylinder. A radiation shields 438 may be provided to capture and
absorb (at least in part) the ASE and fluorescence radiation for
the LGM disks 406a and 406b.
[0038] The circular arrangement of the relay mirror groups causes
the path of laser beam 414 to execute a three-dimensional
trajectory in space. FIG. 7 is a schematic diagram showing the path
of the laser beam though the amplifier assembly. The individual
relay mirrors 418 are labeled 418xy, where the "x" and "y" identify
the mirror location. In particular, "x" is either "a" or "b" and it
corresponds to the location of the relay mirror 418 in the relay
mirror group 404a or 404b, respectively. For example, a mirror
418ay, is in the mirror group 404a. The label "y" identifies the
position of a mirror 418 within its particular relay mirror group.
For example, the relay mirror 418bf, is in the f-position in the
mirror group 404b.
[0039] Referring now to FIG. 8, there is shown a laser oscillator
system 500 in accordance with one embodiment of the subject
invention. The laser amplifier system 500 comprises two solid-state
laser (SSL) amplifiers 502a and 502b, and a multi-pass laser
optical assembly further comprising relay mirrors 518aa, 518ab,
518ba, and 518bb arranged in relay mirror groups 504a and 504b
respectively comprising relay mirrors 518aa and 518ab, and 518ba,
and 518bb. The laser amplifier system 500 further comprises an
outcoupling mirror 556 and an end mirror 554. The end mirror 554
and the outcoupling mirror 556 may be arranged to form a laser
resonator. Such a laser resonator may be either stable or unstable.
In addition, the outcoupling mirror 556 may have a uniform,
partially reflective coating or a graded reflectivity coating. The
SSL amplifiers 502a and 502b may have same construction and
functionality as the SSL amplifiers 302a and 302b of FIG. 3. The
relay mirror groups 504a and 504b together may form a multi-pass
optical assembly.
[0040] In operation, laser diodes 528 inject optical power to the
lasing portions 508 and pump the laser ions to a laser transition,
thus producing laser gain in the lasing portions 508. A laser beam
514 directed into the end mirror 554 is reflected onto the relay
mirror 518aa of the relay mirror group 504a, and therefrom onto the
lasing portion 508 of the LGM disk 506b where the beam is amplified
and reflected to relay mirror 518ab the relay mirror group 504a.
The relay mirror 518ab reflects the laser beam 514 onto relay
mirror 518bb of the relay mirror group 504b, and therefrom onto the
lasing portion 508 of the LGM disk 506a where the beam is amplified
and reflected to relay mirror 318ba of the relay mirror group 504b.
The laser beam 514 may be reflected from relay mirror 518ba onto
the outcoupling mirror 556. A predetermined portion of the laser
beam energy is allowed to pass through the outcoupling mirror 556
and released from the laser system 500 as an output laser beam
514'. The remaining portion of the laser energy is reflected by the
outcoupling mirror 556 back onto the relay mirror 518ba and
retraces its path all the way to the end mirror 554, while being
amplified in the process.
[0041] As in the system 300 of FIG. 3, additional relay mirrors may
be added and the relay mirror 518ba may reflect the laser beam onto
an additional relay mirror. Additional relay mirrors may be added
and receive the laser beam from the relay mirror 518ba. The
additional relay mirrors may be arranged to repeat the process of
passing the laser beam alternately to and from the lasing portions
508 of the two LGM disks 506a and 506b arbitrary number of times
until the desired laser beam amplification is attained before the
beam is delivered to the outcoupling mirror 556 and exits from the
laser system 500.
[0042] The present invention may also be used in commercial
applications, for example, material processing such as cutting,
welding, drilling or like operations. The present invention enables
a very simple, compact and inexpensive solid-state laser system
with average power between about 5 kilowatts and about 15 kilowatts
(although other power ranges may be available) with exceptional
beam quality.
[0043] The terms of degree such as "substantially", "about" and
"approximately" as used herein mean a reasonable amount of
deviation of the modified term such that the end result is not
significantly changed. For example, these terms can be construed as
including a deviation of at least.+-.5% of the modified term if
this deviation would not negate the meaning of the word it
modifies.
[0044] Moreover, terms that are expressed as "means-plus function"
in the claims should include any structure that can be utilized to
carry out the function of that part of the present invention. In
addition, the term "configured" as used herein to describe a
component, section or part of a device includes hardware and/or
software that is constructed and/or programmed to carry out the
desired function.
[0045] The term "suitable", as used herein, means having
characteristics that are sufficient to produce a desired result.
Suitability for the intended purpose can be determined by one of
ordinary skill in the art using only routine experimentation.
[0046] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
the invention. As used herein, the singular forms "a", "an" and
"the" are intended to include the plural forms as well, unless the
context clearly indicates otherwise. It will be further understood
that the terms "comprises" and/or "comprising," and "includes"
and/or "including" when used in this specification, specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof. Although specific embodiments
have been illustrated and described herein, those of ordinary skill
in the art appreciate that any arrangement which is calculated to
achieve the same purpose may be substituted for the specific
embodiments shown and that the invention has other applications in
other environments. This application is intended to cover any
adaptations or variations of the present invention. The following
claims are in no way intended to limit the scope of the invention
to the specific embodiments described herein.
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